Furnaces



Jan. 24, 1961 A. w. FRANK 2,969,412

FURNACES Filed April 9. 1959 2 Sheets-Sheet 1 INVENTOR ARTHUR w FRANK 1961 A. w. FRANK 2,969,412

FURNACES Filed Apz il 9, 1959 2 Sheets-Sheet 2 INVENTOR ARTHURW, FRANK FURNACES Arthur W. Frank, Pewaukee, Wis., assignor, by mesne assignments, to Basic Products Corporation, Milwaukee, Wis., a corporation of Wisconsin Filed Apr. 9, 1959, Ser. No. 805,164

9 Claims. (Cl. 1331) The present invention relates to electric furnaces of the type heated by electrical resistance elements which are located within the furnace and which are connected through openings in the furnace wall to a power source.

In previously available furnaces, the terminal portions extending from each end of the central heating portion of the electrical resistance elements project through openings in opposite walls of the furnace. The ends of the terminal portions with electrical connections at their ends are housed within sealed terminal enclosures attached to opposite furnace walls. The heated furnace atmosphere leaking between the terminal portion and the furnace wall as well as heat developed by the flow of electrical current through the terminal portion is confined within the terminal enclosure, thereby elevating its temperature. Thus, the electrical connections to the resistance elements are subjected to a high degree of heat. Within the terminal enclosure, the heat from the terminal portions of elements at different levels causes convection heat currents. The heat currents can disturb the tem perature uniformity of the furnace wall and therefore the furnace.

- The terminal enclosure prevents the operator from making a simple visual inspection of the ends of the terminal portions and their electrical connections. In order to service a single connection or element it is necessary to disassemble the enclosure and expose all of the connections. The sealed terminal enclosure being subjected to the furnace atmosphere during operation must be carefully purged of the outside atmosphere whenever the furnace is first put into use. Failure to purge the enclosure could result in an explosion resulting from a mixture of the furnace atmosphere and outside atmosphere.

One of the objects of the invention is to provide a seal arrangement for high temperature furnace heating elements which will elfectively seal the element to the furnace wall without subjecting the seal member to excessive temperatures.

Another object of the invention is to provide a seal arrangement for high temperature furnace heating elements which will seal individual elements to the furnace wall.

The invention is particularly adapted for use in an electric furnace containing a gas atmosphere. It includes a furnace wall having an opening and a seal housing with open ends mounted at one end over the wall opening. Electrode means extend through the furnace wall opening and said housing. At the other end of the housing, a flexible sheet sealing member seals the opening between the housing and the electrode means so as to prevent leakage along the electrode means either out of or into the furnace. The sheet may have an aperture through which the electrode means passes.

In a preferred aspect, a tubular housing extending from the wall opening through which the electrode means passes is employed. Cooling means can be provided for the housing. Within the housing and surrounding United States Patent O the electrode means may be provided electrical insulating means such as heat-resistant fiber or a ceramic tube.

These and other objects, features and advantages of the invention will become apparent from the following detailed description and drawings which are merely exemplary.

In the drawings:

Fig. 1 is an enlarged sectional view of the furnace wall and seal;

Fig. 2 is a fragmentary elevational view of the fur-v nace wall and seal with a modified form of cooling; and

insulating heat resistant material may be covered by a metal shell 11. The interior 12 of the furnace may be:

heated by a rod-like resistance element 13 which enters into the furnace through openings 14 and 15 in the.

furnace wall and shell, respectively. The central heating portion 13a of resistance element 13 has a high resistance and this is heated by the electric current to a high temperature. ments 13 have low resistance and thus develop less heat than do the center portions. The heat radiated to furnace wall It by terminal portion 13b helps to heat the furnace. The interior 12 of the furnace, in addition to being subjected to high temperature, may contain a specific gas atmosphere as required by the use of the furnace such as heat treating, high temperature testing, brazing, etc. To withstand the temperature and possible adverse effects of the furnace atmosphere, central heating portion 13a may be constructed of silicon carbide. orother suitable resistance heating material. Ends of terminal portion 13b are metallized to provide a lowcontact resistance metallic surface for flexible terminal clamps 16. Terminal clamps 16 are connected to an electrical power source (not shown). During operation of the furnace, element 13 may move or deflect due to. temperature expansion. Opening 15 in wall 10 is made sufliciently large to permit free movement of element 13. Opening 14 may be made larger than opening 15 so as to insure against a short circuit between element 13 and shell 11 and to minimize heat transfer from the element to the shell.

Seal housing 17 which may be of tubular form is mounted at one end over opening 14 in shell 11 by means of its attaching flange 18 and is held in place by screws 19. Gasket 20 between flange 18 and shell 11 makes the joint leakproof and restricts heat transfer from the housing to the shell. The other end of housing 17 is provided with a flange 21. Seal 22 consisting of one or more flexible sheets 23 and having an aperture 24' through which passes terminal portion 13b of element 13, is mounted on flange 21 so as to close over the open end of the seal housing 17. Seal 22 is held in place on flange 21 by clamping ring 25 which is held by screws 26.

Since it is desirable that the atmosphere of the furnace Patented Jan. 24, 1961- The terminal portions 13b of resistance elerubber. Fig. 3 shows seal 22 deflected to one side following motion of element 13 in response to temperature expansion.

In order to electrically insulate housing 17 from terminal portion 13b, the region between the housing and the terminal portion may be provided with an electrical insulating material 27. Heat developed by the flow of current through the low resistance terminal portions 131) is transferred through electrical insulating material 27 to seal housing 17. This prevents the subjecting of seal 22 to an excessive temperature. The insulating material is sufliciently resilient so that it does not interfere with the movements and deflections of terminal portion 13b. As a further measure to dissipate the heat from terminal portion 13b and to prevent seal 22 from reaching an excessive temperature, cooling fins 28 may be applied to the outside of housing 17. Fig. 2 shows an alternate scheme of cooling for housing 17 in which tube 29 containing a coolant is wrapped around the outside of the housing.

As shown in Fig. 4, the aperture 24 of seal 22 may be surrounded by a torus ring 30 formed in the seal material. Ring 30 serves to strengthen the area of the seal surrounding the aperture 24 so that it is not torn or damaged during installation or removal of seal 22 with respect to terminal portion 13b.

- It should be apparent that variations can be made in the details of construction without departing from the spirit of the invention except as defined in the appended claims.

What is claimed is:

1. In a high temperature furnace including a furnace wall having an opening therein, the combination including a housing having open ends mounted at one end over said opening, an electrode of rod-like forin extending through said furnace opening and said housing, and a flexible sheet member of heat resistant material sealing the opening at the other end of said housing between said housing and said electrode, whereby said electrode is sealed to said furnace.

'2. In a high temperature furnace containing a gas atmosphere including a furnace wall having an opening therein, the combination including a tubular housing'extending from said wall opening, cooling means for said housing, an electrode extending through said wall opening and said housing and a flexible sheet member of heat resistant material having an aperture through which said electrode passes, said flexible sheet member sealing the other end of said tubular housing to said electrode, whereby said electrode is flexibly sealed to said furnace wall while being capable of limited motion.

3. In a high temperature furnace including a furnace wall having an opening therein, the combination including a housing having open ends mounted at one end over said opening, an electrode of rod-like form extending through said furnace opening and said housing, insulating means within said housing and surrounding said electrode, and a flexible sheet member of heat resistant material sealing the opening at the other end of said housing between said housing and said electrode, whereby said electrode is sealed to said furnace.

4. In a high temperature furnace containing an atmosphere including a furnace wall having an opening therein, the combination including a tubular member extending from said wall opening at one end, an electrode extending through said wall opening and said tubular member, insulating material within said tubular member and surrounding said electrode, whereby said electrode is sealed to said furnace wall, and a flexible sheet member of heat resistant material having an aperture through which said electrode passes, said flexible sheet member sealing the other end of said tubular member to said electrode,

whereby said electrode is sealed to said furnace wall.

5. In a high temperature furnace containing a gas atmosphere including a furnace wall having an opening therein, the combination including a tubular housing extending from said wall opening, cooling means for said housing, an electrode extendingthrough said wall opening and said housing, electrical insulating means between said electrode and said housing, and a flexible sheet member of heat resistant material having an aperture through which said electrode passes, said flexible sheet member sealing the other end of said tubular housing to said electrode, whereby said electrode is flexibly sealed to said furnace wall while being capable of limited motion.

6. In a high temperature furnace containing an atmosphere including a furnace wall having an opening therein, the combination including a housing having open ends, one of said ends being mounted over the opening in said wall, fluid cooling means for said housing, a silicon carbide resistor heating element extending through said wall opening and said housing, electrical insulating fibers within said housing and surrounding said heating element, and a diaphragm of silicone rubber material sealing the opening at the other end of said housing, between said element and said housing, whereby said element is sealed to said furnace.

7. in a high temperature furnace including a furnace wall having an opening therein, the combination including a tubular housing mounted at one end over said wall opening, cooling means for said housing, an electrical heating element extending through said wall opening and said housing, electrical insulating material within said housing and surrounding said heating element, and a diaphragm of silicone rubber material, having an aperture through which said element passes and sealing the opening at the other end of said housing between said element and said housing, said diaphragm having the form of a torus ring surrounding said aperture, whereby said element is sealed to said furnace wall.

8. A seal for an electrode extending through an opening in the wall' of an electric furnace including a housing having open ends mounted at one end over said wall opening, said electrode extending through said housing, electrical insulating means within said housing and surrounding said electrode, and a diaphragm means at the other end of said housing, sealing said housing to said electrode, whereby said electrode is sealed in passing through said furnace wall.

9. A seal for an electrical heating element extending through an opening in a partition including a tubular housing mounted at one end over said opening, with said element passing through said housing, electrical insulating,

material within said housing and surrounding said element, heat transfer means surrounding said housing, and a diaphragm having an aperture through which said element passes and sealing said element to said housing, said diaphragm having a torus ring form surrounding said aperture, whereby said element is sealed to said partition.

References Cited in the file of this patent UNITED STATES PATENTS 846,521 Stevens Mar. 12, 1907 2,123,158 Ridgway July 5, 1938 2,180,580 Clark Nov. 21, 1939 2,625,414 Krana Jan. 13, 1953 2,727,936 Boyer Dec. 20, 1955 2,768,277 Buck et a1 Oct. 23, 1956 

